High voltage electrolytic capacitors are employed as energy storage reservoirs in many applications, including implantable medical devices. These capacitors are required to have a high energy density because it is desirable to minimize the overall size of the implanted device. This is particularly true of an implantable cardioverter defibrillator (“ICD”), also referred to as an implantable defibrillator, because the high voltage capacitors used to deliver the defibrillation pulse can occupy as much as one third of the ICD volume. Further, these capacitors experience high levels of shock and vibration conditions such that the capacitors must be adequately stabilized to prevent failure of the capacitors due to movement of, for example, a tantalum anode inside a casing of a wet electrolytic capacitor. Attempts have been made to stabilize the anodes of wet electrolytic capacitors by placing a restraint between the outer surface of the anode pellet and the casing wall. However, such an arrangement requires the use of a larger casing having an increased height in order to accommodate the restraint (e.g., a polymer, glass, or ceramic material), while at the same time still allowing enough room for the working electrolyte to create a sufficient connecting path between the anode and cathode of the capacitor. However, this defeats the purpose of utilizing a planar anode to reduce the overall size of the ICD and results in an undesirable increase in the overall size of the ICD. Further, there may not be sufficient contact between the anode surface and the restraint to effectively stabilize the anode within the capacitor casing.
As such, a need currently exists for an improved wet electrolytic capacitor for use in implantable medical devices, such as defibrillators.